This invention pertains to the art of couplings and, more particularly, to stab-type couplings.
The invention is particularly applicable to a coupling apparatus in which a non-metallic pipe or tube end is received in the apparatus by simply pushing or thrusting the pipe end therein. The pipe end is gripped along an exterior surface by the coupling which resists attempted withdrawal. The invention is particularly applicable to a plastic pipe as utilized in the natural gas industry and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed in other environments and applications.
A typical stab-type coupling is well known in the art. These types of couplings are designed to facilitate ease of installation so that one end of a smooth wall plastic pipe, such as is widely used in the natural gas industry, is severed and simply inserted into the coupling body. No detailed machining or aligning steps are necessary and recent advents in the art have provided a secure coupling arrangement. Nevertheless, a potential problem exists with these type of prior art couplings. There is an extremely remote possibility that slow removal of an inserted plastic pipe into the coupling body can proceed without the gripping portions of the coupling apparatus actively and grippingly engaging the pipe end.
Yet another remote potential exists that a leak path may be established along an exterior surface of the plastic pipe. It is believed that a dimple may be formed in the exterior surface of the pipe due to the creep associated with plastic elements. More specifically, imposition of extreme forces on an external surface of the pipe can leave a dimple or identation therein. If this dimple or identation is positioned adjacent a cut end of the pipe, such as received in the coupling body, the potential exists for a leak path to be established therearound.
U.S. Pat. No. 4,229,025, issued to Volgstadt, et al. on Oct. 21, 1980, illustrates one stab-type coupling. In that arrangement, a spacer ring cooperates with a retaining ring of metallic construction adjacent a flange portion of a hollow stiffener. Additionally, a flexible flange extends inwardly from an outer end of the body to define a cover that prohibits entry of dirt and moisture into the interior of the coupling body. An alternate arrangement of this cover employs a plastic sleeve in conjunction with an O-ring seal.
On the other hand, U.S. Pat. No. 4,445,714, issued to Kisiel, III, on May 1, 1984 illustrates a coupling arrangement in which a spacer retainer ring is interposed between a radially outward extending flange of the hollow stiffener and the retaining collet. This embodiment utilizes a gasket disposed axially outward of the collet for operative engagement with a threaded nut. Inward movement of the nut is designed to apply sealing pressure on the gasket and urge engagement between the collet and locking ring. This type of construction suffers from the absence of a seal located inwardly of the collet for sealing engagement with an external surface of an inserted plastic pipe.
With the foregoing in mind, it is an object of the present invention to provide a new and improved coupling which improves on these prior designs and provides a simple, reliable, and economical coupling apparatus.